The KYC feature can be a positive step to ensure underage children are not involved in gambling. But we must also remember that underage children can find casinos that do not require KYC upon registration and if the children only gamble with small amounts of money, they will be fine. But everything will change when the casino submits a request to perform KYC. That would result in the kids moving on to another casino or even borrowing an adult's ID for verification.
This not entirely true since underage player can always use ID of their parents to verify their account. I’ve done this before on exchange when I’m still underage and doesn’t have valid ID to verify my account. Some parents doesn’t care about KYC since they don’t know much online technology.
The only benefits of KYC for me is the ability to recover my account when it’s hacked since I can prove ownership using my ID that I use to verify my account.